The formation of gaseous giant planets is thought to occur in the first few million years after stellar birth. Models predict that the process produces a deep gap in the dust component (shallower in ...the gas). Infrared observations of the disk around the young star HD 142527 (at a distance of about 140 parsecs from Earth) found an inner disk about 10 astronomical units (AU) in radius (1 AU is the Earth-Sun distance), surrounded by a particularly large gap and a disrupted outer disk beyond 140 AU. This disruption is indicative of a perturbing planetary-mass body at about 90 AU. Radio observations indicate that the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology. The high stellar accretion rate would deplete the inner disk in less than one year, and to sustain the observed accretion matter must therefore flow from the outer disk and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk. Here we report observations of diffuse CO gas inside the gap, with denser HCO(+) gas along gap-crossing filaments. The estimated flow rate of the gas is in the range of 7 × 10(-9) to 2 × 10(-7) solar masses per year, which is sufficient to maintain accretion onto the star at the present rate.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present high-resolution ALMA Band 6 and 7 observations of the tidally disrupted protoplanetary disks of the RW Aurigae binary. Our observations reveal tidal streams in addition to the previously ...observed tidal arm around RW Aur A. The observed configuration of tidal streams surrounding RW Aur A and B is incompatible with a single star-disk tidal encounter, suggesting that the RW Aurigae system has undergone multiple flyby interactions. We also resolve the circumstellar disks around RW Aur A and B, with CO radii of 58 au and 38 au consistent with tidal truncation, and 2.5 times smaller dust emission radii. The disks appear misaligned by 12° or 57°. Using new photometric observations from the American Association of Variable Star Observers (AAVSO) and the All Sky Automated Survey for SuperNovae (ASAS-SN) archives, we have also identified an additional dimming event of the primary that began in late 2017 and is currently ongoing. With over a century of photometric observations, we are beginning to explore the same spatial scales as ALMA.
The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized ...particles are trapped at the location of the continuum peak. In this paper, we present 860 m ALMA observations of polarized dust emission from this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1%-2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼100 m. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both ALMA polarization and previous ALMA and Very Large Array observations, we suggest that the thermal emission at 860 m wavelength is optically thick (τabs ∼ 7.3) at the dust trap with a maximum observable grain size of ∼100 m rather than an optically thin case with centimeter-sized dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 m thermal emission is optically thick.
We present a detailed multiwavelength characterization of the multi-ring disk of HD 169142. We report new Atacama Large Millimeter/submillimeter Array (ALMA) observations at 3 mm and analyze them ...together with archival 0.89 and 1.3 mm data. Our observations resolve three out of the four rings in the disk previously seen in high-resolution ALMA data. A simple parametric model is used to estimate the radial profile of the dust optical depth, temperature, density, and particle size distribution. We find that the multiple ring features of the disk are produced by annular accumulations of large particles, probably associated with gas pressure bumps. Our model indicates that the maximum dust grain size in the rings is ∼1 cm, with slightly flatter power-law size distributions than the interstellar medium-like size distribution (p ∼ 3.5) found in the gaps. In particular, the inner ring (∼26 au) is associated with a strong and narrow buildup of dust particles that could harbor the necessary conditions to trigger the streaming instability. According to our analysis, the snowlines of the most important volatiles do not coincide with the observed substructures. We explore different ring formation mechanisms and find that planet-disk interactions are the most likely scenario to explain the main features of HD 169142. Overall, our multiwavelength analysis provides some of the first unambiguous evidence of the presence of radial dust traps in the rings of HD 169142. A similar analysis in a larger sample of disks could provide key insights on the impact that disk substructures have on the dust evolution and planet formation processes.
ABSTRACT Transitional disks show a lack of excess emission at infrared wavelengths due to a large dust cavity, that is often corroborated by spatially resolved observations at ∼ mm wavelengths. We ...present the first spatially resolved ∼ mm-wavelength images of the disk around the Herbig Ae/Be star, HD 97048. Scattered light images show that the disk extends to 640 au. ALMA data reveal a circular-symmetric dusty disk extending to 350 au, and a molecular disk traced in CO J = 3-2 emission, extending to 750 au. The CO emission arises from a flared layer with an opening angle 30°-40°. HD 97048 is another source for which the large (∼ mm-sized) dust grains are more centrally concentrated than the small (∼ m-sized) grains and molecular gas, likely due to radial drift. The images and visibility data modeling suggest a decrement in continuum emission within 50 au, consistent with the cavity size determined from mid-infrared imaging (34 4 au). The extracted continuum intensity profiles show ring-like structures with peaks at 50, 150, and 300 au, with associated gaps at 100 and 250 au. This structure should be confirmed in higher-resolution images (FWHM 10-20 au). These data confirm the classification of HD 97048 as a transitional disk that also possesses multiple ring-like structures in the dust continuum emission. Additional data are required at multiple and well-separated frequencies to fully characterize the disk structure, and thereby constrain the mechanism(s) responsible for sculpting the HD 97048 disk.
Abstract
As the world-leading submillimeter telescope, the Atacama Large Millimeter/submillimeter Array observatory is now putting more focus on high-frequency observations at Band 7–10 (frequencies ...from 275 to 950 GHz). However, high-frequency observations often suffer from rapid variations in atmospheric opacity that directly affect the system temperature
T
sys
. Current observations perform discrete atmospheric calibrations (Atm-cals) every few minutes, with typically 10–20 occurring per hour for high frequency observation and each taking 30–40 s. In order to obtain more accurate flux measurements and reduce the number of atmospheric calibrations (Atm-cals), a new method to monitor
T
sys
continuously is proposed using existing data in the measurement set. In this work, we demonstrate the viability of using water vapor radiometer (WVR) data to track the
T
sys
continuously. We find a tight linear correlation between
T
sys
measured using the traditional method and
T
sys
extrapolated based on WVR data with scatter of 0.5%–3%. Although the exact form of the linear relation varies among different data sets and spectral windows, we can use a small number of discrete
T
sys
measurements to fit the linear relation and use this heuristic relationship to derive
T
sys
every 10 s. Furthermore, we successfully reproduce the observed correlation using atmospheric transmission at microwave modeling and demonstrate the viability of a more general method to directly derive the
T
sys
from the modeling. We apply the semi-continuous
T
sys
from heuristic fitting on a few data sets from Band 7 to Band 10 and compare the flux measured using these methods. We find the discrete and continuous
T
sys
methods give us consistent flux measurements with differences up to 5%. Furthermore, this method has significantly reduced the flux uncertainty due to
T
sys
variability for one data set, which has large precipitable water vapor fluctuation, from 10% to 0.7%.
The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold ...planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fitted by a broad ring between
$145^{+12}_{-12}$
au and
$429^{+37}_{-32}$
au at an inclination of
$40^{+5}_{-6}{^{\circ }}$
and a position angle of
$51^{+8}_{-8}{^{\circ }}$
. A disc edge at ∼145 au is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.
Abstract
The Atacama Large Millimeter/submillimeter Array high-frequency long-baseline campaign in 2019 (HF-LBC-2019) was arranged to undertake band 9 (690 GHz) and 10 (850 GHz) observations using ...the longest 16 km baselines in order to explore calibration feasibility and imaging capabilities. Observations were arranged using close calibrators between 0° and 4° from the target point-source quasars (QSOs) to also explore subtle effects of calibrator separation angle. A total of 13 observations were made, five using standard in-band observations and eight using the band-to-band (B2B) observing mode, where phase solutions are transferred from a lower frequency band. At bands 9 and 10, image angular resolutions as high as 7 and 5 mas were achieved, respectively. Both in-band and B2B experiments were successful in imaging the target QSOs but with varying degrees of quality. Target image coherence varied between 0.14 and 0.79, driven by the calibrator separation angle and effectiveness of phase referencing despite observing in correct stability conditions. We conclude that the phase rms conditions and calibrator selection, specifically separation angle from the target, must carefully be considered prior to observing in order to minimize imaging defects. For bands 9 and 10, in order to achieve a coherence >0.7 such that the image structure and source flux can be regarded as suitably accurate, a 1° separated calibrator should be used while the phase rms over the phase switching cycle time should ideally be <30°.
Gas has been detected in a number of debris disks. It is likely secondary, i.e., produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk ...around the 15-30 Myr old A-type star HD 32297. We find that C0 is located in a ring at ∼110 au with an FWHM of ∼80 au and has a mass of (3.5 0.2) × 10−3 M⊕. Naively, such a surprisingly small mass can be accumulated from CO photodissociation in a time as short as ∼104 yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C0 and CO observations is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of ∼15 M⊕ Myr−1, much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and rerelease. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.
HD 100546 is a well-studied Herbig Be star-disk system that likely hosts a close-in companion with compelling observational evidence for an embedded protoplanet at 68 AU. We present Atacama Large ...Millimeter/Submillimeter Array observations of the HD 100546 disk which resolve the gas and dust structure at (sub)millimeter wavelengths. The CO emission (at 345.795 GHz) originates from an extensive molecular disk (390 + or - 20 AU in radius) whereas the continuum emission is more compact (230 + or - 20 AU in radius ), suggesting radial drift of the millimeter-sized grains. The CO emission is similar in extent to scattered light images indicating well-mixed gas and micrometer-sized grains in the disk atmosphere. Assuming azimuthal symmetry, a single-component power-law model cannot reproduce the continuum visibilities. The visibilities and images are better reproduced by a double-component model: a compact ring with a width of 21 AU centered at 26 AU and an outer ring with a width of 75 + or - 3 AU centered at 190 + or - 3 AU. The influence of a companion and protoplanet on the dust evolution is investigated. The companion at 10 AU facilitates the accumulation of millimeter-sized grains within a compact ring, asymptotically =20-30 AU, by asymptotically = 10 Myr. The injection of a protoplanet at 1 Myr hastens the ring formation (asymptotically =1.2 Myr) and also triggers the development of an outer ring (asymptotically =100-200 AU). These observations provide additional evidence for the presence of a close-in companion and hint at dynamical clearing by a protoplanet in the outer disk.
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